Production of multilayer papers can either be done by the use of a head-box in a single step or by the use of several headboxes and wires or forming units. The challenge is to produce smooth fibre layers without streaks or fibre flocks, i.e. layers with good formation.
The consistency of a furnish in the headbox is of great importance for obtaining a fibre web with good formation. Higher consistency makes it much more difficult to produce a smooth fibre web since the fibres tend to flock, which can be seen as a cloudy visual appearance in the fibre web sheet, i.e. the formation is not good. The normal consistency of a furnish in a headbox is about 0.5-2%, but some examples of higher consistency has also been described in prior art. One example can be seen in U.S. Pat. No. 4,376,012 which discloses usage of a consistency of about 2-5%.
In papermaking processes there is an ongoing concern to find ways to produce paper or paperboard at reduced costs. One way is to reduce the energy needed for the produced paper or paperboard. Many steps in a production line demands high amounts of energy and reducing the energy demand also decreases the production cost. By increasing the consistency, i.e. by reducing the water content, the dewatering and drying demand is reduced, and thus also the energy needed.
Another way to decrease the production cost is to decrease the amount of the expensive raw material, i.e. fibres in the product. In papermaking, fillers are often added in order to improve the properties of the paper but also to reduce the raw material content and thus also the total cost. When making paperboard, there is an ongoing development to produce a paperboard with high bulk and thus decreased raw material content but without decreasing the strength and thickness of the paperboard to maintain the stiffness in the produced paperboard.
There is, however, a need for an improved process to make a paper or paperboard product which decreases the production cost by reducing both the energy demand and the raw material content.